Method and apparatus for delivering and applying an electrically conductive paint

ABSTRACT

The method of applying an electrically conductive paint of this invention includes delivering paint from a color changer ( 30 ) at ground potential, then electrically isolating the color changer ( 30 ) from the paint in a delivery line ( 100 ), and the delivering the paint through a first delivery line ( 74 ) to an electrically charged paint applicator ( 27 ). In the disclosed embodiment, paint is delivered from the color changer ( 30 ) to a paint cannister ( 34 ) having a piston ( 56 ) and the piston ( 56 ) is then extended to drive paint through the delivery tube ( 74 ) to the applicator ( 27 ) while the paint cannister ( 34 ) is electrically isolated from the color changer ( 30 ).

FIELD OF THE INVENTION

This invention relates to a method and apparatus for delivering andapplying an electrically conductive paint by an electrically chargedpaint applicator which electrically charges the paint at a high voltagereceived from a color changer at ground potential and which electricallyisolates the color changer from the applicator.

BACKGROUND OF THE INVENTION

The automotive industry, for example, now proposes to replace solventbased paint with water based paint to reduce environmental concerns andpollution abatement apparatus. However, water based paint is highlyconductive and in a typical mass production application, the paint isapplied with an electrostatic rotary atomizer which electrically chargesthe paint to improve transfer efficiency. Further, such applicationsrequire rapid switching from one color paint to another using a colorchanger. A color changer is simply a valve system having a number ofports each connected to a source of a different color paint andgenerally also includes a port connected to a source of solvent, whichis typically deionized water for water based paints. The color changermust be at ground potential and the color changer therefore must beelectrically isolated from the applicator at high electrical potential.

The prior art has proposed various methods and apparatus for deliveringand applying conductive liquid coating materials, such as water basedpaint, from a source at ground potential, such as a color changer, withan electrically charged paint applicator, such as an electrostaticrotary atomizer, which electrically isolates the source of liquidcoating at ground potential from the electrically charged paintapplicator, sometimes referred to as a “voltage block.” However, suchvoltage block devices are often complex, expensive, subject to failureand limited in application. The prior art has also proposed electricallyisolating a predetermined quantity or volume of electrically conductivepaint between a front and rear pig in the delivery line between thecolor changer and the applicator which are moved through the deliveryline by pneumatic pressure. This method is also, however, limited inapplication and requires a delivery line of sufficient length such thatthe delivery line is longer than the distance between the front and rearpigs. There is therefore a need for a simple, reliable method andapparatus for conveying and applying a conductive paint from a colorchanger at ground potential to an electrically charged paint applicator,such as an electrostatic rotary atomizer, which avoids the problemsassociated with the prior art as set forth hereinbelow.

SUMMARY OF THE INVENTION

As set forth above, the method and apparatus of this invention isadapted to apply an electrically conductive paint, such as a water basedpaint, to a substrate with an electrically charged paint applicator,such as an electrostatic rotary atomizer, from a source of paint atground potential, particularly, but not exclusively a color changer. Asused herein, the term “paint” includes water based paints and generallyany liquid coating, particularly including coatings for protective ordecorative purposes. The method and apparatus of this invention is,however, particularly directed to the application of an electricallyconductive paint which is applied to a substrate with an electricallycharged paint applicator, such as an electrostatic rotary atomizer, andwherein the source of the electrically conductive paint is at groundpotential. As used herein, the term “color changer,” includes anyvalving system adapted to deliver different paints, as this term isdefined above.

The method of applying an electrically conductive paint to a substrateof this invention is particularly adapted for mass productionapplications, wherein the substrate is located in a confined paint spraybooth and the electrically charged paint applicator is located in thepaint spray booth. In a typical application, the paint applicator may bea robotic paint applicator typically mounted on rails which move withthe substrate, such as an automotive body. However, the paint applicatormay be an electrically charged paint spray gun or overhead or sidemounted electrostatic rotary atomizers of the type presently used inmass production applications including, but not limited to theautomotive industry. As set forth above, the apparatus further includesa color changer, as defined above, at ground potential and theelectrically conductive paint is delivered through a delivery line, suchas a plastic tube, preferably having a friction resistant inner layerand an intermediate dielectric layer, such as polyethylene, to preventarcing.

The method of this invention then includes delivering the electricallyconductive paint from the color changer at ground potential, thenelectrically isolating the color changer from both the delivery line andthe electrically conductive paint. Finally, the method of this inventionincludes delivering the electrically conductive paint through thedelivery line to the electrically charged paint applicator, therebycharging the conductive paint and applying the paint to a substratewhile the color changer is electrically isolated from the paint in thedelivery line. In a preferred embodiment, the conductive paint in thedelivery line is a continuous stream which is electrically charged bythe paint applicator.

One preferred embodiment of the method of this invention includesdelivering the electrically conductive paint from the color changer to apaint cannister through a second delivery line between the color changerand the paint cannister, then electrically isolating the color changerfrom the paint cannister and finally delivering the electricallyconductive paint from the paint cannister to the electrically chargedpaint applicator through the first delivery line described above. In onepreferred embodiment, the second delivery line between the color changerand the paint cannister includes a pig or pigging element driving paintin the second delivery line from the color changer to the paintcannister, wherein the pigging element is driven by a nonconductivefluid, such as air, thereby electrically isolating the color changerfrom the paint cannister. In a preferred embodiment of the method ofthis invention, the paint cannister further includes a piston, whereinthe method of this invention includes retracting the piston in the paintcannister to receive the conductive paint from the color changer, thenextending the piston to drive the conductive paint through the firstdelivery line to the electrically charged paint applicator while thepaint cannister is electrically isolated from the color changer.

In a preferred embodiment of the apparatus of this invention, the pistonof the paint cannister is driven by a servomotor providing very accuratedosing of paint. The first delivery -line between the paint cannisterand the applicator may also include a pigging element which is driven bythe conductive paint from the paint cannister to a pig station adjacentthe applicator. The pigging element is then driven by pneumatic pressurefrom the applicator to adjacent the paint cannister, thereby returningpaint in the first delivery line to the paint cannister and electricallyisolating the applicator from the paint cannister. The paint returned tothe paint cannister can then be returned to the color changer by againextending the piston of the paint cannister.

A preferred embodiment of the apparatus for delivering and applying anelectrically conductive paint of this invention thus includes a paintspray booth, an electrically charged paint applicator located within thepaint spray booth and a color changer at ground potential preferablylocated outside the paint spray booth, which may be conventional asknown by those skilled in this art. The apparatus of this inventionfurther includes at least one paint cannister connected to the colorchanger by the second delivery line described above having a pig orpigging element movable between the color changer and the paintcannister to deliver paint in the second delivery line to the paintcannister and electrically isolate the color changer from the paintcannister following delivery of paint to the paint cannister asdescribed above. The apparatus of this invention also includes a firstdelivery line from the paint cannister to the electrically charged paintapplicator. In a preferred embodiment, the apparatus further includes apig or pigging element in the first delivery line which is pushed by theconductive paint from the paint cannister to the paint applicator. Paintremaining in the first delivery line may then be driven to the paintcannister by the pigging element in the first delivery line by anonconductive fluid, such as pressurized air or pneumatic pressure,wherein the piston in the paint cannister is retracted to receive thepaint and the piston in then extended to return the paint to the colorchanger. As set forth above, the piston of the paint cannister ispreferably driven by a servomotor or the like providing a very accuratemetered volume or dose of paint to the paint applicator, which can bevaried for each application of paint depending upon the application. Inone preferred embodiment of the apparatus of this invention, the colorchanger and at least one paint cannister are located outside the paintbooth in an isolation cabinet preferably formed of an electricallyinsulated or dielectric material.

Other advantages and meritorious features of the method and apparatusfor delivering and applying an electrically conductive paint of thisinvention will be more fully understood from the following descriptionof the preferred embodiments, the appended claims and the drawings, abrief description of which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a paint spray booth illustrating oneembodiment of an exterior isolation cabinet;

FIG. 2 is an enlarged view of the isolation cabinet shown in FIG. 1;

FIG. 3 is a side partially cross-sectioned view of one embodiment of apaint dosing cylinder or cannister illustrated in FIGS. 1 and 2; and

FIGS. 4A to 4H are schematic illustrations of the method of deliveringand applying an electrically conductive paint of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As set forth above, the method and apparatus for delivering and applyingan electrically conductive paint (as defined above) of this inventionmay be utilized in mass production applications, such as illustrated inFIG. 1, wherein electrically conductive paint is applied to a substratein an enclosed clean environment which includes one or several paintapplicators as described below. The paint spray booth 20 is defined byan enclosure wall 22, which may include windows 24 for viewing the paintspray booth and at least one paint applicator, such as the robot paintapplicator 26 illustrated. As will be understood, a conventional paintapplicator is generally mounted on a rail (not shown) which moves withthe substrate, such as an automotive body, to apply electricallyconductive paint through an applicator at high voltage, such as theelectrostatic rotary atomizer 27 illustrated in FIG. 1. In a preferredembodiment of the method and apparatus of this invention, theelectrically conductive paint is electrostatically charged to a highvoltage as it is received through the paint applicator 27 as describedfurther hereinbelow. In one preferred embodiment of the apparatus ofthis invention, the paint cannisters 34 and color changer 30 are locatedoutside the paint spray booth 20 in an electrically insulated isolationcabinet or voltage block module 28 as shown in FIG. 1 and FIG. 2 is anenlarged view of the voltage block module 28 as now described.

The voltage block module or electrical insulation cabinet 28 shown inFIG. 2 includes a color changer 30 which, as described above, includes aplurality of valve modules 32 each connected to a source of differentcolored electrically conductive paint (not shown). This embodiment ofthe voltage block module 28 further includes two paint dosing devices orpaint cannisters 34 each including a pig station 36 connected by supplyor delivery lines 38 to color changer 30 and the applicator 26 shown inFIG. 1 and described further below in regard to FIGS. 4A to 4H. In onepreferred embodiment, the paint cannisters 34 each include a piston 56as described below with respect to FIG. 3 having a servomotor drive 40,such that the cannisters 34 each provide an accurate volume or “dose” ofpaint to the applicator 27 shown in FIG. 1. In a preferred embodiment,the voltage block module is defined by an electrically insulated cabinetframe 42, preferably formed of a nonconductive or electricallyinsulating polymer, such as Delrin®, an acetal polymer available fromDuPont, or other suitable nonconductive polymers. As described furtherin a co-pending application assigned to the assignee of thisapplication, the voltage block module 28 includes resistors 44, such as9 G ohm resistors, solvent cannisters 46 and a hood or enclosure 48which receives the lines from the paint cannisters 34 to the applicator(not shown). The disclosed embodiment of the electrical isolationcabinet or voltage block module 28 further includes a grounding switchcabinet 50 which includes various electrical components, including ahigh voltage cascade or voltage generator 52 and a grounding switch 54.However, in view of the fact that the specific components of theelectrical isolation cabinet or voltage block module 28 does not form apart of this invention, except for the color changer and paint dosingcylinders 34, no further explanation is necessary for completeunderstanding of the invention as claimed.

FIG. 3 illustrates one preferred embodiment of the paint cannister orpaint dosing cylinder 34 shown in FIG. 2. The disclosed embodiment ofthe paint dosing cylinder 34 may correspond to the device disclosed inGerman Patent Application No. DE 10233633 and includes a piston 56connected to a piston guide rod 58, which is connected to a bearing 60and a gear drive 62 connected to a servomotor drive 40. The piston 56reciprocates in a piston cylinder or housing 64 which is preferablyformed of a ceramic material providing electrical isolation for receiptof charged conductive paint as described below. The piston 56 mayfurther include a guide rod 66 as shown. As described above, a preferredembodiment of the paint piston dosing device 34 includes a pig station36 having ports 68 for receipt of the delivery lines 38 shown in FIG. 2.The components of the apparatus illustrated in FIGS. 1 to 3 will be morefully understood from the following description of the method ofdelivering and applying an electrically conductive paint shown in FIGS.4A to 4H described below.

FIGS. 4A to 4H illustrate schematically the apparatus described above,including the paint applicator 27 at high voltage, a color changer 30 atground potential, at least one paint canister or paint dosing cylinder34 including a piston 56, reciprocable in a piston cylinder or housing64 having a piston rod 58 preferably connected to a servomotor drive 40shown in FIG. 3 and a pig station 36 at one end of the piston dosingdevice 34. The housing 64 of the piston dosing device 34 includes aninlet 70 and an outlet 72 in fluid communication with the first deliveryline 74 between the piston dosing device 34 and the applicator 27 andthe inlet 70 is connected by a second delivery line 76 to the colorchanger 30. The disclosed apparatus further includes a second pigstation 78 adjacent the applicator 27 which is connected to the firstdelivery line 74 by a line 80. The color changer also includes a thirdpig station 82 adjacent or located within the color changer 30. As shownin FIG. 4A, the first and second pig stations 36 and 78, respectively,are preferably in the form of trunk lines of the first delivery line 74,such that paint or other fluid can flow from the outlet 72 of the paintcannister or piston dosing device 34 to the applicator 27 through line80 without flowing around the pig or pigging element 84. Similarly, thethird pig station 86 is preferably a trunk line of the second deliveryline 76, such that paint or other fluid can flow from the color changer30 through the second delivery line 76 without flowing past the pig orpigging element 86 in the third pig station 82. However, as describedfurther below, the inlet 70 of the paint cannister or piston dosingdevice 34 may be configured to receive paint around the second piggingelement 86. Further, each of the pig stations 36, 78 and 82 include asource of nonconductive fluid under pressure 88, 90 and 92,respectively, which are controlled by valves 94, 96 and 98,respectively. Having described one preferred embodiment of the apparatusof this invention, the method of delivering and applying an electricallyconductive paint of this invention may now be described with referenceto FIGS. 4A to 4G as described below.

As set forth above, the color changer 30 comprises a series of valveseach having a port connected to a separate source of liquid paint underpressure (not shown) by lines 100A, 100B and 100C. In a typicalapplication, the lines 100A, 100B and 100C are connected to separatesources of liquid paint having different colors for application to asubstrate by applicator 27, such as automotive bodies received throughthe paint spray booth 20 illustrated in FIG. 1. As set forth above, thecolor changer 30 must be at ground potential because the color changeris connected by lines 100A, 100B and 100C to sources of liquid paint.Further, the applicator 27 is at a high voltage or high electricalpotential and applies a high electrical charge to the paint as it isreceived through the applicator 27 and the substrate (not shown) isgenerally at ground potential to improve transfer efficiency. Thus,paint is received through one of the lines 100A, 100B or 100C.

In FIG. 4B, paint “P” is received through line 100A to the color changer30 and the paint is then delivered under pressure through the seconddelivery line 76 to the paint cannister 34. As set forth above, thepiston guide rod 58 may be connected to a servomotor drive 40illustrated in FIGS. 2 and 3, which withdraws the piston 56 to receive apredetermined volume or “dose” of paint in cylinder 64 of the paintpiston dosing device 34 as shown in FIG. 4B. As shown, the first piggingelement 84 is then located in the first pig station 36 and the secondpig or pigging element 86 is then located in the third pig station 82and the pigging elements do not block the flow of paint. The valve 98 inthe third pig station 82 is then opened, driving nonconductive fluid,such as air “A,” from the source 92 against the second pigging element86, which drives the second pigging element through the second deliveryline 76 to the paint dosing device 34, driving conductive paintP-remaining in the second delivery line 76 to the paint cannister orpaint dosing device 34 as shown in FIG. 4C, thereby electricallyisolating or creating a voltage block “B” between the color changer 30and the paint cannister 34 as illustrated by the arrows in FIGS. 4C to4E. As the second pigging element 86 is moved to the paint cannister 34,the piston 56 is simultaneously withdrawn to fully charge the paintcannister or dosing device 34 as shown in FIG. 4C. As will beunderstood, however, the piston 56 may be controlled to deliver anypredetermined volume or dose of paint for delivery to the applicator 27,as now described.

While the paint cannister or dosing device 34 is electrically isolatedfrom the color changer 30, as shown by “B”, the piston 56 is thenreversed, driving paint P through the first delivery line 74 and line 80to the applicator 27, thereby electrically charging the paint andapplying the paint through the applicator 27 to a substrate (not shown)in the paint spray booth 20 shown in FIG. 1. In this embodiment, thevalve 94 to the source of nonconductive fluid 88 is opened to drive thefirst pigging element 84 ahead of the paint P as the paint is drivenfrom the paint cannister 34 to the applicator 27, thus receiving thefirst pigging element 84 in the second pig station 78 as shown in FIG.4D. Alternatively, the pigging element 84 may remain in the first pigstation 36 and pneumatic pressure may then be utilized from source 88 todrive paint remaining in the first delivery line 74 to the paintapplicator 27. In the embodiment disclosed, upon completion of the firstpaint cycle, the valve 96 is open to the source of nonconductive fluid90, driving the first pigging element 84 from the second pig station 78adjacent the applicator 27 to the first pig station 36 adjacent thepaint dosing device 34, thereby returning paint P remaining in the firstdelivery line 74 to the paint dosing device 34 as shown in FIG. 4E. Thepaint applicator 27 is thus electrically isolated from the paintcannister forming a voltage block “B” as shown in FIG. 4F. The piston 56in the paint dosing device 34 is simultaneously retracted to receive thepaint P delivered from the first delivery line 74 by the first piggingelement 84. The piston 56 of the paint dosing device 34 is then extendedagain, driving paint from the paint cannister or piston dosing device 34to the color changer 30 and through line 100A to the original source ofconductive paint as shown in FIG. 4F. Finally, the second piggingelement 86 is driven through the second delivery line 76 from adjacentthe paint cannister or piston dosing device 34 to the color changer,returning the paint in the second delivery line 76 to the color changer30 and from the color changer to the source of liquid paint through line100A by driving the second pigging element 86 through the seconddelivery line 76 as shown in FIGS. 4G and 4H.

As will be understood from the above description, the method of thisinvention includes delivering electrically conductive paint P from thecolor changer 30 and then electrically isolating the color changer 30from the electrically conductive paint P, then delivering theelectrically conductive paint through the first delivery line 74 to theelectrically charged paint applicator 27, thereby electrically chargingthe electrically conductive paint. In one preferred embodiment, theconductive paint is a continuous stream to the applicator 27 in thedelivery line 74 as shown, for example, in FIGS. 4D and 4E. In apreferred embodiment of the method of this invention, the electricallyconductive paint is first delivered to a paint cannister, such as thepiston dosing device 34 as shown in FIG. 4C and the color changer 30 isthen electrically isolated from the piston dosing device 34 as shown inFIG. 4C. In the disclosed embodiment, the color changer 30 iselectrically isolated from the piston dosing device 34 by driving thesecond pigging element 86 through the second delivery line 76, forming avoltage block B as shown in FIG. 4C. As will be understood by thoseskilled in this art, however, the color changer 30 may be electricallyisolated from the piston dosing device 34 by pneumatic pressure,although a pigging element 86 is shown is preferred. The paint P is thendriven by the piston 56 to the electrically charged applicator 27through line 74 as shown in FIG. 4D while the color changer 30 iselectrically isolated from the electrically conductive paint and thepiston dosing device 34.

As will be understood by those skilled in this art, variousmodifications may be made to the method and apparatus for delivering andapplying an electrically conductive paint of this invention within thepurview of the appended claims. For example, the piston dosing device orpaint cannister 34 may be eliminated, provided the color changer iselectrically isolated from the first delivery line 74 and the paint Pcontained therein prior to delivery paint to the electrically chargedapplicator 27. Although a piston dosing device of the general type ispreferred, the first delivery line 74 may be of any length, including acoil, providing sufficient length to provide a voltage block as byutilizing a second pigging element 86 as described above. Further, thefirst pigging element 84 may be utilized to deliver paint remaining inthe first delivery line 74 to the paint applicator 27, rather thanreturning the paint to the color changer 30 as described above. Havingdescribed preferred embodiments of the method and apparatus fordelivering and applying electrically conductive paint of this invention,the invention is now claimed as follows.

1. A method of applying an electrically conductive paint to a substrate located in a paint spray booth with an electrically charged paint applicator located within said paint spray booth from a color changer at ground potential, said method comprising the following steps: delivering electrically conductive paint through a first delivery line from said color changer at ground potential to a paint cannister located outside said paint spray booth having a reciprocable piston and retracting said piston to receive a predetermined volume of electrically conductive paint in said paint cannister; then electrically isolating said color changer from said paint cannister and said electrically conductive paint in said paint cannister; and then delivering said electrically conductive paint through a second delivery line from said paint cannister located outside said paint spray booth to said electrically charged paint applicator located within said paint spray booth by extending said piston to drive a predetermined volume of electrically conductive paint from said paint cannister to said electrically charged paint applicator, thereby electrically charging said electrically conductive paint and applying said electrically conductive paint to said substrate with said color changer electrically isolated from said paint cannister and said electrically conductive paint.
 2. The method of applying an electrically conductive paint to a substrate as defined in claim 1, wherein said color changer is connected to said paint cannister by said first delivery line having a pig movable in said first delivery line, said method including moving said pig from adjacent said color changer to adjacent said paint cannister, thereby delivering said electrically conductive paint to said paint cannister and electrically isolating said color changer from said paint cannister.
 3. The method of applying an electrically conductive paint to a substrate as defined in claim 2, wherein said method includes driving said pig from adjacent said color changer to adjacent said paint cannister with a non-conductive fluid.
 4. The method of applying an electrically conductive paint to a substrate as defined in claim 2, wherein said method includes delivering a predetermined volume of said electrically conductive paint from said color changer to said paint cannister through said first delivery line, then driving said pig through said first delivery line with a nonconductive fluid from adjacent said color changer to adjacent said paint cannister to deliver said electrically conductive paint in said first delivery line to said paint cannister and electrically isolate said color changer from said paint cannister.
 5. The method of applying an electrically conductive paint to a substrate as defined in claim 1, wherein said method includes delivering said electrically conductive paint under pressure from said paint cannister to said electrically charged paint applicator within said paint booth through said delivery line in a continuous stream, electrically charging said electrically conductive paint in said delivery line only when said color changer is electrically isolated from said delivery line and said electrically charged paint.
 6. A method of applying an electrically conductive paint to a substrate located in a paint spray booth with an electrically charged applicator located within said paint spray booth from a color changer at ground potential through a delivery line, said method comprising the following steps: delivering said electrically conductive paint under pressure through a first line from said color changer at ground potential to a paint cannister; then electrically isolating said color changer from said paint cannister and said electrically conductive paint in said paint cannister by driving a pig with nonconductive fluid pressure through said first line from said color changer to said paint cannister; then delivering said electrically conductive paint through a second delivery line from said paint cannister to said electrically charged paint applicator, electrically charging said electrically conductive paint and applying said charged electrically conductive paint to said substrate.
 7. The method of applying an electrically conductive paint to a substrate as defined in claim 6, wherein said method includes driving a second pig from said electrically conductive paint applicator to said paint cannister following applying paint to said substrate with a nonconductive fluid to electrically isolate said electrically charged paint applicator from said paint cannister prior to delivering a second paint from said color changer to said paint cannister.
 8. An apparatus for applying an electrically conductive paint to a substrate, comprising: a paint spray booth; an electrically charged paint applicator within said paint spray booth; a color changer located outside said paint spray booth at ground potential; at least one paint cannister having a reciprocable piston; a first delivery line from said paint cannister to said electrically charged paint applicator adapted to deliver electrically conductive paint to said electrically charged paint applicator; and a second delivery line between said paint cannister and said color changer having a pig movable therein between said color changer and said paint cannister to deliver paint in said second delivery line to said paint cannister and electrically isolate said color changer from said paint cannister and said electrically conductive paint when paint is delivered from said paint cannister to said electrically charged paint applicator, charging said electrically conductive paint.
 9. The apparatus for applying an electrically conductive paint as defined in claim 8, wherein said paint cannister is located outside said paint spray booth in an electrically insulated cabinet.
 10. The apparatus for applying an electrically conductive paint as defined in claim 8, wherein said paint cannister includes an inlet communicating with said second delivery line, an outlet communicating with said first delivery line, and said piston movable within said paint cannister adapted to move away from said inlet upon receipt of said electrically conductive paint from said color changer and move toward said outlet to drive electrically conductive paint under pressure through said first delivery line to said electrically charged paint applicator.
 11. The apparatus for applying an electrically conductive paint as defined in claim 10, wherein said piston is driven by a servomotor.
 12. The apparatus for applying an electrically conductive paint as defined in claim 8, wherein said apparatus includes a second paint cannister having a reciprocable piston connected to said color changer by a third delivery line having a pig movable between said color changer and said second paint cannister to deliver electrically conductive paint from said color changer to said second paint cannister and electrically isolate said color changer from said second paint cannister following delivery of electrically conductive paint to said 